1. Field of the Invention
This invention relates to an inflatable ball, more particular to an inflatable ball having dual bladders enclosed in an outer cover.
2. Description of the Related Art
As shown in FIG. 1, a conventional inflatable ball includes an outer cover 1, a rubber bladder layer 2, and a valve unit 3 provided on the rubber bladder layer 2 and extending through the outer cover 1 and the rubber bladder layer 2. The valve unit 3 includes a base portion 301 connected to the rubber bladder layer 2 and a valve portion 302 inserted into the base portion 301. However, the conventional inflatable ball has following disadvantages. The inflatable ball tends to lose its desired shape by virtue of the material employed for the rubber bladder layer 2 (i.e., vulcanized rubber) when the rubber bladder layer 2 is over-inflated. Moreover, the rubber bladder layer 2 is made from a single layer of rubber, so that a leakage problem is likely to occur. In addition, since the base portion 301 of the valve unit 3 is made from an elastic rubber material, the valve portion 302 is likely to be moved through the base portion 301 and thus falls into the rubber bladder layer 2 when being inserted into the base portion 301.
FIG. 2 shows another conventional inflatable ball, which includes an outer cover 1, a rubber bladder unit 2, and a valve unit 3 provided on the rubber bladder unit 2 and extending through the outer cover 1 and the rubber bladder unit 2. The rubber bladder unit 2 includes a rubber layer 201 and a winding thread 202 wound around the rubber layer 201. The valve unit 3 includes a base portion 301 and a valve portion 302 inserted into the base portion 301. The winding thread 202 prevents over-inflation of the rubber layer 201. However, the requirement for a winding apparatus makes the manufacture of the inflatable ball complicated, and the problem of uneven winding and the problem of falling of the valve portion 302 from the base portion 301 are likely to occur.
FIG. 3 shows yet another conventional inflatable ball, which includes an outer cover 1, a rubber bladder unit 2, and a valve unit 3 provided on the rubber bladder unit 2 and extending through the outer cover 1 and the rubber bladder unit 2. The rubber bladder unit 2 includes a rubber layer 201 and fabric tapes 202 provided on the rubber layer 201. The valve unit 3 includes a base portion 301 and a valve portion 302 inserted into the base portion 301. The fabric tapes 202 prevent over-inflation of the rubber layer 201. However, the fabric tapes 202 have a problem of uneven tension, so that the shape and size of the inflatable ball cannot be desirably maintained. Furthermore, the procedure for attaching the fabric tapes 202 to the rubber layer 201 is complicated. The problem of falling of the valve portion 302 from the base portion 301 is also likely to occur in this inflatable ball.